Catheters and dilators for trans-septal procedures and methods for making and using them

ABSTRACT

Devices and methods are provided for performing a medical procedure using a trans-septal approach. The device includes a dilator including a proximal end, a distal end terminating in a distal tip, and a lumen extending between the dilator proximal and distal ends, and a needle device including a proximal end, a distal end sized for introduction into the dilator lumen and terminating in a sharpened distal tip. The needle is movable relative to the dilator to selectively expose the needle device distal tip distally from the dilator lumen and advance the dilator relative to the needle device. The dilator may have a complex tapered shape on its distal tip, e.g., including first and second tapered regions. The needle device may include an inner needle including the sharpened distal tip and an outer tube including a substantially blunt distal end that slidably receives the inner needle.

RELATED APPLICATION DATA

This application claims benefit of provisional application Ser. No.61/820,993, filed May 8, 2013, and 61/912,503, filed Dec. 5, 2013, theentire disclosures of which are expressly incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention relates generally to apparatus, systems, andmethods for performing medical procedures, and, more particularly, todilators, needles, and access devices for accessing a body lumen withina patient's body, and to methods for making and using such devices.

BACKGROUND

Various medical procedures involve accessing a chamber of the heartusing a trans-septal approach. For example, a guide catheter or sheathmay be introduced into the right atrium of a patient's heart, e.g., froma percutaneous access site, and a Brockenbrough needle may be introducedthrough the guide sheath and advanced through the intra-atrial septum ofthe heart into the left atrium. A guidewire may be then introducedthrough the needle into the left atrium, whereupon the needle may beremoved.

One or more dilators may be advanced over the guidewire (or over theneedle before removal) to dilate the puncture through the septum, e.g.,to create a passage sufficiently large to introduce the guide sheaththrough the puncture in the septum. The dilator provides a transition tobridge the diameter difference between the guidewire and the outerdiameter of the guide sheath. The taper provided on the tip of suchdilators is generally a substantially uniform conical ramp, and thelonger the taper (i.e., the more shallow the angle), the lower theaxially-applied axial force needed to apply the same radial dilationforce against the tissue surrounding the puncture.

However, if the length of dilator tip is too long, it may present asafety risk, such as left atrial perforation or other damage to tissue.For example, a dilator taper may be too long for a number of reasonsincluding 1) it is so long that it touches undesired anatomy before theguide sheath can access the desired space (e.g., the left atrial wall,vessel bifurcation, and the like) or 2) in the follow-through thatfrequently happens (e.g., when the insertion force drops dramaticallywhen fully dilated to the sheath diameter) the dilator tip may touchand/or damage undesired anatomy.

One or more instruments may then be introduced through the guide sheathand/or over the guidewire into the left atrium, e.g., to perform aprocedure within the left atrium or other region of the heart accessedvia the left atrium.

Additionally, there is a need for devices that facilitate accessing bodylumens, such as chambers of the heart using trans-apical approachesand/or other puncture techniques, e.g., to perform medical procedurestherein, while reducing the risk of undesired punctures or tissuedamage.

SUMMARY

The present invention is directed to apparatus, systems, and methods forperforming medical procedures. More particularly, the present inventionis directed to dilators, needles, and access devices for accessing abody lumen within a patient's body, e.g., accessing a chamber of theheart across a septum of the heart, to systems including such devices,and to methods for making and using such devices.

In an exemplary embodiment, a method is provided for performing amedical procedure within a patient's body, e.g., involving accessing achamber of the heart using a trans-septal approach. Generally, a distalend of a tubular sheath is introduced into a first body lumen, e.g.,into the right atrium or other chamber of the patient's heart, and aneedle device may be used to puncture a septum or other tissue wall tocreate a puncture therethrough communicating with a second body lumen,e.g., the left atrium or other adjacent chamber of the heart. A dilatormay be advanced over the needle device through the tissue wall, therebydilating tissue surrounding the puncture, and a procedure sheath, e.g.,the tubular sheath, may be advanced over the dilator through the dilatedpuncture into the second body lumen. Optionally, a guidewire may beintroduced through the puncture, e.g., via the needle device, thedilator, and/or the sheath. One or more instruments may be introducedthrough the sheath into the second body lumen to perform a medicalprocedure.

When the dilator is advanced through the puncture, the tissue dilationforces applied to the tissue surrounding the puncture, as a function ofdiameter, may not be linear. Generally speaking, tissue dilation forcesare, on average, smallest in the initial semi-elastic range of thetissue and increase non linearly outside of the initial elastic range.In an exemplary embodiment, the tip of the dilator may include a taperconfiguration to facilitate advancement and/or minimize “jumping” (whenthe dilator tip clears the tissue, which may otherwise cause the distaltip to advance suddenly into the second body lumen). For example, thedilator tip may include multiple tapered regions having different taperangles, e.g., a relatively steep initial tapered region at thedistal-most region of the tip, and a longer and/or relatively smallertapered region proximal to the distal-most region. For example, thedilator tip may be configured to provide a substantially consistent“axial dilation force,” i.e., the linear pushing encountered by theoperating physician may be substantially constant as the dilator tip isadvanced through the tissue to dilate the puncture.

In accordance with another embodiment, an access device is provided thatincludes a dilator comprising a proximal end, a distal end sized forintroduction into a patient's body and terminating in a distal tiphaving a complex tapered shape, and a lumen extending between thedilator proximal and distal ends; and a needle device comprising aproximal end, a distal end sized for introduction into the dilator lumenand terminating in a sharpened distal tip, the needle movable relativeto the dilator to selectively expose the needle device distal tipdistally from the dilator lumen and advance the dilator relative to theneedle device. In one embodiment, the dilator distal tip may include adistal-most region have a first linear taper defining a first anglerelative to a longitudinal axis of the dilator, and a second regionadjacent the distal-most region having a second liner taper defining asecond angle relative to the longitudinal axis, the second angle beingsmaller than the first angle. In another embodiment, the dilator distaltip may include a continuously variable curved taper.

In accordance with yet another embodiment, a method is provided forperforming a medical procedure within a patient's body that includesintroducing a distal end of a tubular sheath into a first body lumen;advancing a distal end of a needle device from the distal end of thesheath through a tissue wall into a second body lumen; advancing adistal end of a dilator over the needle device through the tissue wall,thereby dilating tissue surrounding the puncture using a complex shapedtapered distal tip of the dilator; and advancing the sheath distal endover the dilator through the dilated puncture into the second bodylumen. In an exemplary embodiment, the complex shaped tapered distal tipmay be shaped to provide a substantially consistent axial dilation forcewhen the complex shaped tapered distal tip is advanced through thetissue wall to dilate the puncture.

In accordance with still another embodiment, an access device isprovided for performing a medical procedure using a trans-septalapproach that includes a dilator comprising a proximal end, a distal endsized for introduction into a patient's body and terminating in atapered distal tip, and a lumen extending between the dilator proximaland distal ends; an outer tube comprising a proximal end, a distal endsized for introduction into the dilator lumen and terminating in asubstantially blunt distal tip, and a lumen extending between the outertube proximal and distal ends; and a needle comprising a proximal end, adistal end sized for introduction into the outer tube lumen andterminating in a sharpened distal tip, wherein the needle is movablerelative to the outer tube to selectively expose the needle distal tipdistally from the outer tube lumen and retract the needle distal tipinto the outer tube lumen, and wherein the dilator is movable relativeto the outer tube for advancing the dilator distal tip relative to theouter tube.

In accordance with another embodiment, a system is provided forperforming a medical procedure using a trans-septal approach thatincludes a tubular sheath comprising a proximal end, a distal end sizedfor introduction into a patient's body, and a lumen extending betweenthe sheath proximal and distal ends; a dilator comprising a proximalend, a distal end sized for introduction into the sheath lumen andterminating in a tapered distal tip, and a lumen extending between thedilator proximal and distal ends; an outer tube comprising a proximalend, a distal end sized for introduction into the dilator lumen andterminating in a substantially blunt distal tip, and a lumen extendingbetween the outer tube proximal and distal ends; and a needle comprisinga proximal end, a distal end sized for introduction into the outer tubelumen and terminating in a puncturing distal tip, wherein the needle ismovable relative to the outer tube to selectively expose the needledistal tip distally from the outer tube lumen and retract the needledistal tip into the outer tube lumen, and wherein the dilator is movablerelative to the outer tube and the sheath for advancing the dilatordistal tip relative to the outer tube.

In accordance with still another embodiment, a method is provided forperforming a medical procedure within a patient's body that includesintroducing a distal end of a tubular sheath into a first body lumen;advancing a distal end of an outer tube from the distal end of thesheath within the first body lumen; pressing the outer tube distal endagainst a tissue wall within the first body lumen; with an inner needlepositioned within the outer tube such that a sharpened distal tip of theneedle is positioned adjacent the outer tube distal end and the tissuewall, retracting the outer tube, thereby impaling the tissue wall on thesharpened distal tip and directing the sharpened distal tip through thetissue wall into a second body lumen and creating a puncture through thetissue wall; and advancing the outer tube distal end over the needlethrough the puncture and into the second body lumen.

Other aspects and features of the present invention will become apparentfrom consideration of the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate exemplary embodiments of the invention, inwhich:

FIG. 1 is a perspective view of an exemplary embodiment of a system forperforming a medical procedure using a trans-septal approach thatincludes a guide sheath, dilator, and needle device.

FIG. 2 is an exploded view of an exemplary embodiment of an accessdevice that may be included in the system of FIG. 1 in which the needledevice includes an inner needle and an outer tube.

FIGS. 3A-3D are cross-sectional views of a patient's heart showing amethod for accessing a chamber of the heart trans-septally using theaccess device of FIG. 2.

FIG. 4A is a side view of an exemplary embodiment of a dilator.

FIG. 4B is a partial cross-sectional view of a region of the dilator ofFIG. 4A showing an exemplary construction of the dilator.

FIGS. 5A and 5B are details showing exemplary distal tips that may beprovided on a dilator, such as that shown in FIG. 4A.

FIGS. 6A and 6B are details comparing the distal tip of FIG. 5A with asimple tapered distal tip.

FIGS. 6A(1)-6B(2) are graphs comparing forces experienced when using thedistal tips of FIGS. 6A and 6B to dilate a puncture through tissue.

FIG. 7 is a side view of another exemplary embodiment of a system forperforming a medical procedure using a trans-septal approach thatincludes a guide sheath, dilator, and needle.

FIGS. 8A and 8B are side views of alternative embodiments of dilatorsthat may be included in the system of FIG. 7.

FIGS. 9A-9C are cross-sectional details of alternative embodiments ofdilator-needle devices including different configurations of cooperatingstops on the dilator and needle.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Turning to the drawings, FIG. 1 shows an exemplary embodiment of asystem 10 for performing a diagnostic and/or therapeutic procedurewithin a patient's body, e.g., within a chamber of a heart accessedusing a trans-septal approach. In the embodiment shown, the system 10includes a guide sheath, catheter, or other tubular member 20, e.g., forintroducing one or more devices into a patient's body to perform aprocedure, and a trans-septal access device 30 that may be introducedthrough the guide sheath 20, e.g., to puncture or otherwise penetratethrough a tissue structure to provide access to a body lumen beyond thetissue structure, e.g., to access a chamber of a heart from an adjacentchamber, as described further below. Generally, the access device 30includes a needle device 40 and a dilator 60 slidable relative to oneanother, such as any of the embodiments described elsewhere herein.

FIG. 2 shows an exemplary embodiment of an access device 30 that may beused in conjunction with the guide sheath 20, which includes an innerneedle 40, an outer tube 50, and a dilator 60, which may telescopedrelative to one another, i.e., allowing the needle 40 to be removablyinserted into the outer tube 50, and the outer tube 50 to be removablyinserted into the dilator 60, allowing the components of the accessdevice 30 to remain slidable relative to one another during a procedure.

The components of the system 10, e.g., the guide sheath 20, needle 40,outer tube 50, and dilator 60, may have lengths sufficient to beintroduced from an access site, e.g., a percutaneous access site intothe patient's vasculature, into a target body lumen, e.g., the rightatrium or other chamber of the heart. The relative lengths of thecomponents may allow tips of the needle 40, outer tube 50, and/or thedilator 60 to be exposed a desired distance and/or retracted into thesurrounding device, as described further below. In exemplaryembodiments, the components of the system 10 may have a length betweenabout twenty and one hundred twenty centimeters (20-120 cm) with thelengths varying relative to one another by a predetermined distance,e.g., to allow distal tips of the components to be deployed from thesurrounding component a desired distance during use. Optionally, one ormore of the components may include stops and/or other features, whichmay limit relative movement of the telescoped components relative to oneanother, e.g., on or in the distal ends and/or on the handles or hubs(not shown), as described elsewhere herein.

The inner needle 40 is generally an elongate solid or hollow needleincluding a proximal end 42 with a hub or handle 43, a distal end 44terminating in a sharpened distal tip 45, thereby defining alongitudinal axis 12 therebetween. Optionally, the needle 40 may includea guidewire lumen (not shown) extending between the proximal and distalends 42, 44, e.g., to allow a guidewire or other rail (also not shown)to be advanced through the needle 40, e.g., after puncturing the septumto allow the rail to be introduced into a target chamber beyond theseptum.

In exemplary embodiments, the distal tip 45 may be pointed, beveled,and/or otherwise sharpened to allow the distal tip 45 to puncturethrough tissue, such as the intra-atrial septum (not shown), asdescribed elsewhere herein. Alternatively, the distal tip 45 and/ordistal end 44 adjacent the distal tip 45 may include one or morefeatures to facilitate puncturing and/or other otherwise directing thedistal tip 45 through tissue. For example, one or more helical threads(not shown) may be provided along a desired length of the distal end 44from the distal tip 45, e.g., to allow the distal tip 45 to be threadedinto and through tissue and/or unthreaded back through the tissue, asdesired.

The needle 40 may be formed from metal, e.g., stainless steel, and/orother materials having sufficient column strength to allow the distaltip 45 to be advanced to puncture tissue from the proximal end 42without buckling or kinking. For example, the needle 40 may be formedfrom a single solid or tubular wire, hypo-tube, and the like having asubstantially uniform diameter or other cross-section along its lengthand/or having a variable cross-section along its length. The distal end44 of the needle 40 may be biased to a substantially straightconfiguration, yet may be resiliently directed into a curved or othershape, e.g., when positioned with the outer tube 50 and/or othercomponents of the access device 30.

The outer tube 50 may be constructed generally similar to the needle 40,e.g., including a proximal end 52 (optionally, including a hub or handle53), a distal end 54 sized for introduction into the guide sheath 20,and a lumen 56 extending therebetween sized for slidably receiving theneedle 40. Unlike the needle 40, the outer tube 50 may terminate in asubstantially blunt distal tip 55 and/or may include one or moreelements (not shown) on the distal tip 55 for releasably biting into orotherwise engaging tissue without puncturing entirely through thetissue. Alternatively, the distal tip 55 may be formed from relativelysoft and/or atraumatic material, e.g., to prevent the distal tip 55 frompuncturing and/or otherwise damaging tissue when the distal tip 55 ispressed or otherwise directed against tissue, as described furtherelsewhere herein.

In exemplary embodiments, the outer tube 50 may formed from a stainlesssteel hypo-tube or other tubular body, e.g., having sufficient columnstrength to allow the distal tip 55 to be pressed against tissue, e.g.,to cause the septum to tent or be subjected to tension to facilitatepuncturing the septum using the needle 40, as described elsewhereherein. Optionally, as shown, the distal end 54 of the outer tube 50 maybe bent, curved, or biased to other non-linear shapes, e.g., immediatelyadjacent the distal tip 55, yet may be resiliently straightened, e.g.,when positioned within the dilator 60 and/or guide sheath 20 duringintroduction. In an alternative embodiment, the outer tube 50 may beomitted and the needle 40 may be provided directly within the dilator 60or the dilator 60 may be advanced directly over the needle 40 withoutany intervening devices therebetween.

The dilator 60 is also a generally tubular member including a proximalend 62, a distal end 64, and a lumen 66 extending therebetween. Thedilator 60 may terminate in a substantially atraumatic distal tip 65,e.g., including a predetermined taper or other shape, as describedelsewhere herein. In addition or alternatively, the distal end 64 of thedilator 60 may include a predetermined curve, bend, and/or othernon-linear shape, yet may be resiliently straightened, bent further, andthe like, for example, to facilitate introduction of the dilator 60,e.g., through tortuous anatomy and/or over the needle 40 and/or outertube 50.

Optionally, the dilator 60 may include one or more markers (not shown)on the distal end 64, e.g., to facilitate positioning and/or otherwisemonitoring the dilator 60 using external imaging, such as fluoroscopy,ultrasound, and the like. In an exemplary embodiment, a plurality ofmarkers may be provided on the distal end 64 that are spaced apartaxially from one another. If the distal end 64 includes a curve or bend,the markers may be arranged asymmetrically relative to the periphery ofthe distal end 64, e.g., to facilitate identifying the rotationalorientation of the distal end 64 using external imaging. For example, aplurality of markers may be provided on only one side of the distal end64, e.g., on the outside of the bend or curve, to identify the locationand orientation of the distal end 64.

The dilator 60 may be formed from various materials, such as polymers orother plastics, e.g., HDPE, UHMWPE, PTFE, Nylon, harder grades of PEBA,urethanes, and the like. Optionally, one or more coatings, e.g., ofhydrophilic, silicone, and/or other materials may be provided along theinner surface defining the lumen 66 and/or along at least part of theouter surface, e.g., to facilitate introduction of the needle 40 and/orouter tube 50 therethrough and/or sheath 20 thereover. Alternatively,the dilator 60 may be formed from multiple layers and/or segments ofmaterials having different mechanical properties than one another and/ormay include a liner, e.g., a hydrophilic or lubricious material and/or abraid or coil of metal or polymeric material, that may reduce the riskof the needle 40 and/or outer tube 50 skiving or otherwise damaging theinner surface, e.g., similar to other embodiments herein.

Returning to FIG. 1, the guide sheath 20 may be any conventionalcatheter or sheath including a proximal end 22, a distal end 24 sizedfor insertion into a body lumen, a lumen 26 extending between theproximal and distal ends 22, 24, and a central longitudinal axis 28extending between the proximal and distal ends 22, 24. The lumen 26 mayexit at or communicate with an outlet 27 in the distal end 24, e.g., toallow the access device 30, a guidewire, and/or other instrument (notshown) to be introduced therethrough. The distal end 24 may include atapered, rounded, or otherwise shaped distal tip 25, e.g., to provide asubstantially atraumatic tip and/or to facilitate advancement ornavigation through various anatomy.

Optionally, the proximal end 22 may include a handle or hub 23, e.g.,configured and/or sized for holding and/or manipulating the guide sheath20 from the proximal end 22. In addition, the handle 23 may include oneor more ports, e.g., a port 23 a communicating with the lumen 26 andincluding one or more valves, e.g., a hemostatic valve (also not shown),which may provide a substantially fluid-tight seal, while accommodatinginsertion of one or more instruments into the lumen 26. In addition, asshown, the handle 23 may include an infusion port 23 b, e.g., forcoupling a source of fluid (not shown) to the handle 23 to deliversaline or other fluids into the lumen 26, e.g., around the dilator 60,needle 40, and/or other instruments (not shown) positioned within thelumen 26.

Generally, the guide sheath 20 may include an inner liner, e.g., atleast partially or entirely surrounding or otherwise defining the lumen26, a reinforcement layer surrounding the inner liner, and an outerjacket surrounding the reinforcement layer, each of which may extend atleast partially between the proximal and distal ends 22, 24 of the guidesheath 20. The reinforcement layer and/or outer jacket may be attachedto the inner liner, e.g., by laminating, adhering, adhesive bonding,ultrasonic welding, reflowing or other heating, and the like, asdescribed elsewhere herein.

In an exemplary embodiment, the lumen 26 is defined by an inner linerincluding an inner surface, e.g., formed from lubricious material.Alternatively, the inner liner may be formed from one or more layers ofthermoplastic or other polymeric material including one or more coatingson the inner surface having desired properties, e.g., a hydrophilicand/or lubricious coating, e.g., similar to the liners disclosed in U.S.Pat. Nos. 7,550,053 and 7,553,387, and U.S. Publication No.2009/0126862, the disclosures of which are expressly incorporated byreference herein.

Optionally, any or all of the inner liner, reinforcement layer, and/orouter jacket may be formed from multiple layers of like or differentmaterials (not shown), e.g., to provide desired material properties inthe different portions of the guide sheath 20. In an exemplaryembodiment, the outer jacket may be formed from PEBAX, nylon, urethane,and/or other thermoplastic material, e.g., such that the material of theouter jacket 44 may be heated and reflowed and/or otherwise formedaround the components defining the lumen 18.

In one embodiment, one or more of the layers of the guide sheath 20 mayhave a substantially homogenous construction between the proximal anddistal ends 22, 24. Alternatively, the construction may vary along thelength of the guide sheath 20 to provide desired properties. Forexample, a proximal portion of the guide sheath 20 adjacent the proximalend 12 may be substantially rigid or semi-rigid, e.g., providingsufficient column strength to allow the distal end 14 of the guidesheath 20 to be pushed or otherwise manipulated from the proximal end22, while a distal portion may be substantially flexible.

The reinforcement layer may include one or more reinforcing members,e.g., wound in a braided or other helical configuration around the innerliner, and the outer jacket may include one or more tubular layerssurrounding the reinforcement layer and/or between the reinforcementlayer and the inner liner. In an exemplary embodiment, the reinforcementlayer may include one or more, or a plurality of, round or flat (e.g.,rectangular, elliptical, or flat oval) wires, filaments, strands, orother reinforcement members, e.g., formed from metal, such as stainlesssteel, plastic, glass, woven or twisted fibers, such as aramid, and thelike, or composite materials.

Turning to FIGS. 3A-3D, an exemplary method is shown for using theaccess device 30 of FIG. 2 to provide trans-septal access within apatient's heart 90, e.g., across the intra-atrial septum 92 betweenchambers of the heart 90, for example, from the right atrium 94 into theleft atrium 96. Initially, as shown in FIG. 3A, the distal end 24 of theguide sheath 20 may be introduced into the patient's body, e.g., intothe patient's vasculature from a percutaneous access site in a femoralvein, left or right internal or external jugular vein, subclavian vein,axillary vein, and the like. For example, the distal end 24 may beadvanced and/or otherwise manipulated until the distal tip 25 ispositioned within the right atrium 94 adjacent the septum 92, e.g.,adjacent a target puncture site to access the left atrium 96.

The needle 40, outer tube 50, and dilator 60 may be preloaded within thelumen 26 of the guide sheath 20 with the distal tips 45, 55, 65positioned within the lumen 26, e.g., adjacent the distal tip 27 of theguide sheath 20 during introduction of the guide sheath 20.Alternatively, the needle 40, outer tube 50, and/or dilator 60 mayinserted into the guide sheath 20 after positioning the distal end 24within the right atrium 94. In this alternative, the dilator 60 may beinserted first and then the needle 40 and outer tube 50 may be insertedinto the dilator 60 together or sequentially.

If the outer tube 50 and needle 40 are introduced together into thedilator 60 or guide sheath 20, the outer tube 50 may protect the innersurface of the dilator lumen 66 and/or guide sheath lumen 26. Forexample, the needle tip 45 may be positioned within the outer tube lumen54 adjacent the outer tube tip 55, and the needle 40 and outer tube 50may be inserted together into the dilator lumen 64. In thisconfiguration, the outer tube 50 covers the needle tip 45, preventingthe needle tip 45 from contacting the inner surface, which may otherwiseskive and/or remove pieces of the dilator 60 and/or guide sheath 20,which may be released into the right atrium 94 where they may risksubstantial harm to the patient.

Turning to FIG. 3B, with the distal tip 25 of the guide sheath 20adjacent the septum 92, the outer tube 50 may be advanced, e.g., todeploy the distal end 54 of the outer tube 50 within the right atrium 94and/or press the distal tip 55 against the septum 92, e.g., to cause thetissue of the septum 92 to “tent” or otherwise become subjected totension away from the right atrium 94, as shown. Optionally, the distaltip 55 may otherwise engage the wall of the right atrium 94 withoutpuncturing the septum 92, e.g., to couple the outer tube 50 to theseptum 50.

With reference to FIG. 3C, the needle 40 may be positioned such that thedistal tip 45 is immediately adjacent the distal tip 55 of the outertube 50 (if not already positioned at this location), and the outer tube50 may be retracted proximally. This action may reveal or expose thedistal tip 45 of the needle 40 from the outer tube 50 and pull theseptum 92 proximally and/or permit the release of built up tension inthe septum 92, thereby causing the septum 92 to impale over the distaltip 45 and/or driving the distal end 44 of the needle 40 through theseptum 92, e.g., until the distal end 44 enters the left atrium 96.Thus, in this method, the needle 40 may not be advanced to puncture theseptum 92, e.g. but the needle 40 remains substantially stationary whilethe septum 92 moves from left to right onto and/or over the needle 40,which may reduce the risk of over-advancement or “jumping” of the needle40 and/or undesired movement of the tissue.

Optionally, the outer tube 50 may be advanced over the needle 40 todirect the distal end 54 of the outer tube 50 through the puncture inthe septum 92 into the left atrium 96. The needle 40 may then beremoved, leaving the distal end 54 of the outer tube 50 within the leftatrium 96 to provide subsequent access. Thus, given that the distal tip55 of the outer tube 50 does not include a sharp, puncturing tip likethe needle 40, a sharp object is not presented within the left atrium 96for the subsequent steps of the procedure, which may reduce the risk ofinjury to tissue within the left atrium 96. Optionally, the distal end54 and/or distal tip 55 may be made soft or compliant, e.g., by a lasercut pattern, material transition, addition of a polymer tip, and thelike. Alternatively, the distal end 54 and/or distal tip 55 may includea shape, e.g., to cause it to be less traumatic and/or anchor aftercrossing into the left atrium 96, e.g., such as a coil, helix and/orbend (not shown). One or more devices (not shown) may be delivered andor monitoring performed, e.g., pressure transduction, and the likethrough the lumen 56 of the outer tube 50.

In addition or alternatively, a guidewire (not shown) may be introducedthrough the access device 30 into the left atrium, e.g., through theneedle 40 if it includes a guidewire lumen or through the lumen 56 ofthe outer tube 50 after removing the needle 40. Optionally, once the tipof the guidewire is positioned within the left atrium 96, the outer tube50 may be removed, thereby leaving the guidewire extending from theguide sheath 20 through the puncture in the septum 92 into the leftatrium 96.

The dilator 60 may then be introduced into the guide sheath 20 (orsimply advanced if already positioned within the guide sheath 20), e.g.,over the guidewire, or alternatively over the outer tube 50 and/orneedle 40 if not removed. The distal end 64 of the dilator 60 may beexposed from the guide sheath 20 within the right atrium 94 and advancedinto the puncture to dilate the tissue of the septum 92 surrounding thepuncture. Optionally, the tapered shape of the distal tip 65 of thedilator may be selected to facilitate insertion through the septum 92and/or dilation of tissue without substantial risk of jumping or otherover-advancement of the dilator 60 when the distal end 64 clears theseptum 92 and enters the left atrium 96, e.g., as described furtherelsewhere herein.

As described elsewhere herein, the dilator 60 may provide a transitionfrom the relatively small outer diameter or profile of the guidewire (orouter tube 50 or needle 40 if not removed) to the relatively largerouter diameter or profile of the guide sheath 20. Thus, once the largerdiameter region of the distal end 64 of the dilator 60 is advancedcompletely through the septum 92 into the left atrium 96, the puncturemay be dilated to a diameter substantially similar to the outer profileof the guide sheath 20 (or alternatively another procedure sheath, notshown, which may be advanced through the guide sheath 20 or may replacethe guide sheath 20). The guide sheath 20 may then be advanced throughthe septum 92 to position the distal tip 25 of the guide sheath 20within the left atrium 96. The dilator 60 (and outer tube 50 or needle40 if not already removed) may then be withdrawn into the guide sheath20 and removed completely from the patient's body.

With the guide sheath 20 and/or guidewire positioned within the leftatrium 96, the sheath lumen 26 may then be used to introduce one or moreinstruments (not shown) into the left atrium 96 to perform one or moreprocedures within the left side of the heart, e.g., within the leftatrium 96 itself or the left ventricle (not shown). Once the desiredprocedure(s) are completed, the instrument(s) may be removed and thenthe guide sheath 20 and guidewire may also be removed. The puncture inthe septum 92 may be closed using conventional devices and methods,e.g., via the guide sheath 20 and/or guidewire before their removal.

Turning to FIGS. 4A and 4B, an exemplary embodiment of a dilator 60 isshown, which may be included in the access device 20 and/or system 10(not shown) described elsewhere herein. In the embodiment shown, thedilator 60 is formed from different materials having different materialproperties, e.g., at different locations along the length of the dilator60 and/or in different layers of the dilator 60.

For example, as shown in FIG. 4A, the dilator 60 may be configured toprovide different stiffnesses at different axial locations on thedilator 60, e.g., a proximal end 62 that is substantially rigid and/orsemi-rigid to facilitate advancement of the distal end 64 withoutsubstantial risk of the dilator 60 buckling or kinking. In addition, adistal-most region of the tapered distal tip 65 may also be formed fromsubstantially rigid, semi-rigid, or relatively stiff material, e.g., toensure that the distal-most region holds its shape when advanced throughtissue, e.g., surrounding a septal puncture, at a percutaneous accesssite, and the like. A proximal region of the tapered distal tip 65and/or a predetermined length of the distal end 64 may be formed fromflexible and/or relatively soft material, e.g., to allow the distal end64 to bend during introduction through tortuous anatomy. Optionally, afurther proximal region (not shown) may be formed from a relativelystiffer material to provide pushability and/or support.

In addition or alternatively, as shown in FIG. 4B, the dilator 60 may beformed from a plurality of layers having different mechanicalproperties. For example, the dilator 60 may include a relatively thininner layer 70 of relatively hard and/or abrasion resistant material,e.g., HDPE, UHMWPE, PTFE, nylon, harder grades of PEBA or urethanes, andthe like, surrounded by a relatively thick outer layer 74 of relativelysoft material, e.g., PEBAX, urethane, and the like. Optionally, asshown, an intermediate bond layer 72, e.g., to enhance bonding the innerand outer layers 70, 74 together, e.g., including Plexar, Oravec, andthe like. Alternatively, the inner and outer layers 70, 74 may beattached directly to one another, e.g., by one or more of melting,reflowing, sonic welding, heat welding, and the like.

In one embodiment, the inner layer 70 may extend substantially theentire length of the dilator 60, e.g., entirely between the proximal anddistal ends 62, 64, while one or more material may be used for the outerlayer 74, e.g., to vary the rigidity/flexibility along its length. Theinner layer 70 may provide desired stiffness and/or abrasion resistanceto protect the inner surface of the dilator 60, e.g., when a needledevice (not shown) is introduced through the dilator lumen 66, therebyreducing the risk of skiving and/or removing pieces of the dilator 60,e.g., when a sharpened tip of a needle is advanced through the dilatorlumen 60, particularly if the dilator 60 is positioned in a curved orother nonlinear orientation within a patient's anatomy. In particular,HDPE may provide a substantially low friction surface for use as a linerfor a dilator 60 used with a stainless steel needle that preventssubstantial risk of skiving.

The outer layer 74 may increase the flexibility of the dilator 60, e.g.,compared to forming the dilator 60 entirely from HDPE or otherrelatively stiff materials. Using relatively softer, flexible materialsfor the outer layer 74 may enhance pushability of the dilator 60, e.g.,through tortuous anatomy. In exemplary embodiments, the inner layer 70may have a thickness between about 0.001 to 0.025 inch (0.025-0.625 mm)and the outer layer 74 may have a thickness substantially greater thanthe inner layer 70, e.g., between about 0.005 to 0.15 inch (0.125-3.75mm).

Optionally, the inner surface of the inner layer 70 may be coated withone or more materials, e.g., a silicone, hydrophilic, and/or othercoating, as described elsewhere herein for other embodiments, to reducefriction and/or otherwise facilitate inserting needle devices throughthe dilator 60. In addition or alternatively, the inner layer 70 mayinclude one or more additional structures, e.g., a braid or coil ofmetal or polymeric material, which may be substantially abrasionresistant and/or reduce friction for devices inserted through thedilator 60.

Turning to FIGS. 5A and 5B, any of the dilators herein may include atapered distal end having a complex shaped taper, e.g., designed totransform non-linear tissue dilation function for a given tissue into asubstantially more constant axial dilation force, e.g., for one or moreof the benefits described elsewhere herein, within a given lengthconstraint. For example, FIG. 5A shows an exemplary embodiment of adistal end 64A of a dilator 60A having a uniform outer diameter and atapered distal tip 65A including two substantially linear tapers. Asshown, the tapered distal tip 65A includes a distal-most region 65A-1having a first taper of a relatively steep angle relative to alongitudinal axis 68 and an adjacent region 65A-2 having a second taperof a more shallow angle. For example, in the embodiment shown, thedistal-most region 65A-1 may have a length L1 and transition from asmallest diameter D1 to an intermediate diameter D2, and the adjacentregion 65A-2 may have a length L2 and transition from the intermediatediameter D2 to an outer diameter D3 of the dilator 60A. Thus, in thisembodiment, the tapers may be configured such that (D2−D1)/L1 is greaterthan (D3−D2)/L2, while L1+L2 may be less than or equal to the totallength of a simple/conventional dilator taper while maintaining orreducing axial puncture force, e.g., to reduce the risk of damagingtissue within a body lumen within which the distal tip 65A is advanced.For example, a multi-region taper may be made shorter than a simpletaper while producing similar or lower axial puncture forces, or amulti-region taper may be made equivalent in length to a simple taperwhile producing lower axial puncture forces.

Optionally, the distal-most region 65A-1 may be formed from desiredmaterials for the dilator 60A, such as those described elsewhere herein,optionally without any external coating, and the adjacent region 65A-2may be formed from the same or different materials than the distal-mostregion 65A-1, but with an external coating, as shown, e.g., ahydrophilic and/or lubricious coating.

Additionally, where the relatively steeper angle of the distal-mostregion 65A-1 may generate greater axial dilation forces, the diameter D2may be set within the elastic range of the tissue being dilated, and themore shallow angle and/or coating of the adjacent region 65A-2 mayreduce the axial dilation forces, e.g., to provide a net effect thatsubstantially homogenizes the overall axial force encountered by theuser when the dilator 60A is advanced through a puncture to dilatetissue surrounding the puncture, as described elsewhere herein.

It will be appreciated that more than two substantially linear taperedregions may be provided on the distal tip 65A, if desired, with eachregion having a smaller taper angle (relative to the longitudinal axis68) and/or longer length than the distally adjacent region. As shown,the tapered regions may be disposed immediately adjacent one another.Alternatively, if desired, a substantially uniform diameter region (notshown) may be provided between differently tapered regions.

Turning to FIG. 5B, another embodiment of a distal end 64B of a dilator60B is shown that includes a more complex design for the tapered distaltip 65B. In this embodiment, the distal tip 65B includes a continuouslyvariable curve, which may vary substantially smoothly along the lengthof the distal tip 65B, e.g., according to the specific tissue dilationforces of target tissue. Optionally, the geometric force transformingelements provided by the complex tapered distal tip may be furtherenhanced or normalized, e.g., by providing one or more coatings and/ormaterial layers, including hydrophobic and hydrophilic materials. Forexample, an area of relatively high tissue dilation force may benormalized (e.g., relative to the initial elastic range) by the additionof these coatings or materials and/or via a geometric transformation.

Turning to FIGS. 6A and 6B, a complex shaped distal tip of a dilator 60A(shown in FIG. 6B) is compared to a single taper tip 6 of a conventionaldilator (shown in FIG. 6A). FIGS. 6A(1)-6B(2) show graphs demonstratingqualitatively the forces likely encountered when using the respectivedilator tips to dilate a puncture through tissue. For example, FIG.6A(1) demonstrates that the axial dilation force necessary to use thedilator tip 6 to dilate a puncture increases significantly as the singletaper tip 6 is advanced through the tissue, e.g., due to the increasingresistance of the tissue to dilation after its initial elastic range. Incontrast, FIG. 6A(2) demonstrates that the axial dilation force usingthe dilator 60A may be more consistent as the complex tapered tip 65A isadvanced through the tissue, e.g., with the relatively shallow taper ofthe adjacent region 65A-2 requiring a substantially lower force than thesingle taper tip.

Similarly, FIGS. 6B(1) and 6B(2) demonstrate that the risk of “jumping”or over-advancement of the dilator 60A may be substantially reducedcompared to the single taper tip 6. For example, once the single tapertip 6 completely exits the puncture, the resistance to advancement maybe substantially reduced due to the uniform profile of the adjacentregion. This unexpected change may cause the user to advance the dilator6 substantially before being able to reduce the axial force. Incontrast, given the shallow taper of the adjacent region 65A-2 of thecomplex dilator tip 65A, the change in resistance to advancement whenthe distal tip 65A completely exits the puncture may be less, therebyreducing the risk of the user over-advancing the distal tip 65A.

Turning to FIG. 7, another exemplary embodiment of a system 110 is shownthat includes a guide sheath 120 and an access device 130, e.g.,including a dilator 160 and a needle device 140, generally similar toother embodiments herein. Unlike other embodiments, the dilator 160includes one or more stops and/or interlock elements 163, e.g., forselectively coupling the dilator 160 to the guide sheath 120 and/or theneedle device 140. For example, the dilator 160 may include first andsecond interlock elements 163a, 163c spaced apart from one another on aproximal end 162 of the dilator 160. The first interlock element 163 amay couple with a corresponding interlock element 123 a on a handle 123of the sheath 120 and the second interlock element 163 c may couple to ahub 143 on a proximal end 142 of the needle 140. This may, for example,allow the length of the guide sheath 120 to be made shorter, e.g., forlength compatibility with delivery of specific devices (e.g., ballooncatheters, ablation catheters, and the like, not shown), whilepreserving length compatibility of the dilator 160 with a generallylonger needle device 140, and/or with commonly available puncturedevices, including Brockenbrough needles, RF puncture devices, and thelike (also not shown).

Optionally, in any of the embodiments herein, one or more stops may beprovided for limiting relative motion of a needle and dilator, e.g.,when the needle is used to create a puncture through a tissue structure.For example, as shown in FIG. 9A, shows an exemplary embodiment of anaccess device including a needle 240 and a dilator 260, which may begenerally constructed and used similar to other embodiment herein.Unlike other embodiments, the needle 240 and dilator 260 include stops249 a, 269 a fixed at predetermined locations thereon. For example, anannular stop 269 a may be provided within the dilator lumen 266 a, e.g.,spaced proximally from the dilator distal tip 265 a by a predetermineddistance. Similarly, the needle 240 may include an annular stop 249 aspaced proximally from the needle distal tip 245 a. The stops 249 a, 269a may be attached to the needle 240 a and dilator 260 a by one or moreof bonding with adhesive, fusing, sonic welding, soldering, cooperatingconnectors (not shown), and the like, or may be integrally formedtherein.

The stops 249 a, 269 a may be positioned to limit the distance that theneedle distal tip 245 a may be advanced from the dilator lumen 266 a.For example, with the stops, a user may advance the needle 240 a rapidlyrelative to the dilator 260 a, e.g. to enhance puncturing the needledistal tip 245 a through a tissue wall with the stops 249 a, 269 apreventing the distal tip 245 a from being over-advanced into the bodylumen beyond the tissue wall

Optionally, at least one of the stops may be adjustable, e.g., to allowa user to adjust the deployment distance of the needle. For example,FIG. 9C shows another embodiment of a needle 240 c and dilator 260 c inwhich the stop 249 c on the needle 240 c is adjustable axially relativeto the needle distal end 244 c. For example, the needle 240 c and stop249 c may include cooperating threads 284 c that allow the stop 249 c tobe threaded axially along the needle distal end 244 c, e.g., betweenpredetermined proximal and distal positions. For example, the needle 240c may be rotated relative to the stop 249 c (which may be movableaxially but not rotatable within the dilator lumen 266 c), therebythreading the stop 249 c along the needle distal end 244 c.

Turning to FIG. 9B, another embodiment of a needle 240 b and dilator 260b that may include cooperating stops 249 b, 269 b similar to the otherembodiments above. In addition, the needle 240 b and dilator 260 b mayinclude an impulse device, e.g., a spring 282 b coupled between theneedle 240 b and dilator 260 b, e.g., between the needle stop 249 b andan anchor 280 b on the dilator 260 b. The spring 282 b may be used toeject the needle distal tip 245 b from the dilator 260 b, e.g., with thestops 249 b, 269 b limiting the distance that the needle distal tip 245b is deployed. For example, the needle 240 b may be directed proximallyto compress the spring 282 b and store a predetermined level ofpotential energy such that, when the needle 240 b is released, thespring 282 b may be deploy the needle distal tip 245 b from the dilator260 b with sufficient force to puncture entirely through a tissue wall,while the stops 249 b, 269 b prevent the needle distal tip 245 b frombeing deployed beyond the predetermined distance, thereby reducing therisk of accidentally contacting undesired tissue with the needle distaltip 245 b. It will be appreciated that these different configurations ofstops and/or impulse devices may be included in any of the embodimentsdescribed herein.

The foregoing disclosure of the exemplary embodiments has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.Many variations and modifications of the embodiments described hereinwill be apparent to one of ordinary skill in the art in light of theabove disclosure.

Further, in describing representative embodiments, the specification mayhave presented the method and/or process as a particular sequence ofsteps. However, to the extent that the method or process does not relyon the particular order of steps set forth herein, the method or processshould not be limited to the particular sequence of steps described. Asone of ordinary skill in the art would appreciate, other sequences ofsteps may be possible. Therefore, the particular order of the steps setforth in the specification should not be construed as limitations on theclaims.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the scope ofthe appended claims.

We claim:
 1. An access device for performing a medical procedure using atrans-septal approach, comprising: a dilator comprising a proximal end,a distal end having a uniform outer diameter sized for introduction intoa patient's body and terminating in a tapered distal tip, and a lumenextending between the dilator proximal and distal ends, the dilatordistal tip tapering inwardly from the uniform outer diameter, whereinthe distal tip has a complex tapered shape comprising a distal-mostregion having a first linear taper defining a first angle relative to alongitudinal axis of the dilator, and a second region adjacent thedistal-most region having a second linear taper defining a second anglerelative to the longitudinal axis, the second angle being smaller thanthe first angle; an outer tube comprising a proximal end, a distal endsized for introduction into the dilator lumen and terminating in asubstantially blunt distal tip, and a lumen extending between the outertube proximal and distal ends; and a needle comprising a proximal end, adistal end sized for introduction into the outer tube lumen andterminating in a sharpened distal tip, wherein the needle is movablerelative to the outer tube to selectively expose the needle distal tipdistally from the outer tube lumen and retract the needle distal tipinto the outer tube lumen, and wherein the dilator is movable relativeto the outer tube for advancing the dilator distal tip relative to theouter tube.
 2. The device of claim 1, wherein the outer tube comprises astainless steel hypotube extending between the proximal and distal ends.3. The device of claim 2, wherein the distal tip of the outer tubecomprises a polymeric material.
 4. The device of claim 1, wherein theneedle comprises stainless steel.
 5. The device of claim 1, wherein thedistal-most region has a first length and the second region has a secondlength longer than the first length.
 6. The device of claim 1, whereinthe distal-most region has a length L1 and transitions from a firstdiameter D1 to an intermediate diameter D2, and the second region has alength L2 and transitions from the intermediate diameter D2 to an outerdiameter D3 of the dilator, and wherein the regions are configured suchthat (D2−D1)/L1 is greater than (D3−D2)/L2.
 7. The device of claim 1,wherein the dilator comprises an inner layer defining an inner surfaceof the dilator lumen and an outer layer surrounding the inner layer, theinner layer having a greater hardness than the outer layer.
 8. Thedevice of claim 7, wherein inner layer has a smaller thickness than theouter layer.
 9. The device of claim 1, wherein the dilator includesfirst and second interlock elements spaced apart from one another on theproximal end of the dilator.
 10. The device of claim 9, wherein thefirst interlock element is located to couple with a correspondinginterlock element on a sheath through which the dilator is introducedand the second interlock element is located proximal to the firstinterlock element to couple to a hub on the proximal end of the needle.11. The device of claim 1, wherein the distal-most region provides arelatively steep initial tapered region at the distal-most region of thetip, and the second region provides a relatively smaller tapered regionproximal to the distal-most region.
 12. A system for performing amedical procedure using a trans-septal approach, comprising: a tubularsheath comprising a proximal end, a distal end sized for introductioninto a patient's body, and a lumen extending between the sheath proximaland distal ends; a dilator comprising a proximal end, a distal endhaving a uniform outer diameter sized for introduction into the sheathlumen and terminating in a tapered distal tip, and a lumen extendingbetween the dilator proximal and distal ends, the dilator distal tipcomprising a distal-most region tapering inwardly from the uniform outerdiameter, wherein the distal tip has a first linear taper defining afirst angle relative to a longitudinal axis of the dilator, and a secondregion adjacent the distal-most region having a second linear taperdefining a second angle relative to the longitudinal axis, the secondangle being smaller than the first angle; an outer tube comprising aproximal end, a distal end sized for introduction into the dilator lumenand terminating in a substantially blunt distal tip, and a lumenextending between the outer tube proximal and distal ends; and a needlecomprising a proximal end, a distal end sized for introduction into theouter tube lumen and terminating in a puncturing distal tip, wherein theneedle is movable relative to the outer tube to selectively expose theneedle distal tip distally from the outer tube lumen and retract theneedle distal tip into the outer tube lumen, and wherein the dilator ismovable relative to the outer tube and the sheath for advancing thedilator distal tip relative to the outer tube.
 13. The system of claim12, wherein the outer tube comprises a stainless steel hypotubeextending between the proximal and distal ends.
 14. The system of claim13, wherein the distal tip of the outer tube comprises a polymericmaterial.
 15. The system of claim 12, wherein the needle comprisesstainless steel.
 16. The system of claim 12, wherein the distal-mostregion has a first length and the second region has a second lengthlonger than the first length.
 17. The system of claim 12 , thedistal-most region has a length L1 and transitions from a first diameterD1 to an intermediate diameter D2, and the second region has a length L2and transitions from the intermediate diameter D2 to an outer diameterD3 of the dilator, and wherein the regions are configured such that(D2−D1)/L1 is greater than (D3−D2)/L2.
 18. The system of claim 12,wherein the dilator comprises an inner layer defining an inner surfaceof the dilator lumen and an outer layer surrounding the inner layer, theinner layer having a greater hardness than the outer layer.
 19. Thesystem of claim 18, wherein inner layer has a smaller thickness than theouter layer.
 20. The device of claim 12, wherein the dilator includesone or more stops or interlock elements for selectively coupling thedilator to one or both of the tubular sheath and the needle.
 21. Thedevice of claim 20, wherein the dilator includes one or more interlockelements that allow a length of the tubular sheath to be made shorterwhile preserving length compatibility of the dilator with a relativelylonger needle.
 22. The device of claim 20, wherein the one or moreinterlock elements include first and second interlock elements spacedapart from one another on the proximal end of the dilator.
 23. Thedevice of claim 22, wherein the first interlock element is located tocouple with a corresponding interlock element on the proximal end of thesheath and the second interlock element is located proximal to the firstinterlock element to couple to a hub on the proximal end of the needle.24. An access device for performing a medical procedure using atrans-septal approach, comprising: a dilator comprising a proximal end,a distal end having a uniform outer diameter sized for introduction intoa patient's body and terminating in a distal tip having a complextapered shape, and a lumen extending between the dilator proximal anddistal ends, the dilator distal tip tapering inwardly from the uniformouter diameter, wherein the distal tip comprises a distal-most regionhaving a first linear taper defining a first angle relative to alongitudinal axis of the dilator, and a second region adjacent thedistal-most region having a second linear taper defining a second anglerelative to the longitudinal axis, the second angle being smaller thanthe first angle; and a needle device comprising a proximal end, a distalend sized for introduction into the dilator lumen and terminating in asharpened distal tip, the needle movable relative to the dilator toselectively expose the needle device distal tip distally from thedilator lumen and advance the dilator relative to the needle device. 25.The device of claim 24, wherein the needle device comprises stainlesssteel.
 26. The device of claim 24, wherein the distal-most region has afirst length and the second region has a second length longer than thefirst length.
 27. The device of claim 24, the distal-most region has alength L1 and transitions from a first diameter D1 to an intermediatediameter D2, and the second region has a length L2 and transitions fromthe intermediate diameter D2 to an outer diameter D3 of the dilator, andwherein the regions are configured such that (D2−D1)/L1 is greater than(D3−D2)/L2.
 28. The device of claim 24, wherein the dilator comprises aninner layer defining an inner surface of the dilator lumen and an outerlayer surrounding the inner layer, the inner layer having a greaterhardness than the outer layer.
 29. The device of claim 28, wherein innerlayer has a smaller thickness than the outer layer.
 30. The device ofclaim 24, wherein the dilator comprises interlock elements forselectively securing the dilator relative to a hub on a sheath proximalend and a hub on the needle device proximal end.
 31. The device of claim24, wherein the needle device comprises a stop that limits advancementof the needle distal tip beyond the dilator distal end to apredetermined distance.
 32. The device of claim 24, wherein the needledevice comprises an impulse device for applying a predetermined distalforce to the needle distal end to puncture the needle distal tip througha tissue wall and limit advancement of the needle distal end to apredetermined distance beyond the dilator distal end.
 33. The device ofclaim 24, further comprising a tubular sheath comprising a proximal end,a distal end sized for introduction into a patient's body, and a lumenextending between the sheath proximal and distal ends for receiving thedilator and needle device.
 34. The device of claim 33, wherein thedilator includes one or more stops or interlock elements for selectivelycoupling the dilator to one or both of the sheath and the needle device.35. The device of claim 33, wherein the dilator includes one or moreinterlock elements that allow a length of the tubular sheath to be madeshorter while preserving length compatibility of the dilator with arelatively longer needle.